Key establishment selling out-of-this-world drinks? (5,3)
I believe the answer is:
space bar
'key' is the definition.
(space bar is a kind of key)
I don't understand the rest of the clue.
(Other definitions for space bar that I've seen before include "The biggest typewriter key" , "Largest typewriter key" , "Long key on a typewriter" , "It is found on a keyboard" , "Longest typing key" .)